To identify whether exercise promotes coronary collateral formation more dogs will be chronically instrumented with pressure catheters and flow probes. Coronary flow will be measured at rest and during treadmill running. After the initial experiments dogs will be randomly divided into two groups, one to perform daily treadmill running and the other to serve as sedentary controls. After 10-12 weeks coronary collateral flow and hemodynamics will again be measured. In this fashion it will be possible to determine whether exercise can induce collateral development. Because certain vasodilatory stimuli are known to cause maldistribution of coronary flow in animals with stenotic coronary vessels by inducing a coronary steal, the effect of exercise, a potent metabolic vasodilating force, will be examined. Dogs will be instrumented with a small catheter in a branch of the left circumflex coronary artery (LCf). The left anterior descending coronary artery (LAD) will be ligated after the first diagonal branch. The effects of both adenosine and treadmill running on coronary flow, especially that to the LAD myocardium beyond the ligature, will be studied.